1 Field of the Invention
The present invention relates to a stereoscopic system which stereoscopically displays images shot by a three-dimensional camera in a head mounted display, and more specifically, to the setting of the convergence and focus position of the camera and the setting of the convergence and dioptric power of the display.
2. Description of the Prior Art
A stereoscopic system has conventionally been known for viewing images shot by a three-dimensional camera with a three-dimensional viewing apparatus. The three-dimensional camera shoots an object with its left and right cameras to provide left and right images with parallax. The three-dimensional viewing apparatus displays the left and right images and directs them to the left and right eyes to provide a stereoscopic image of the object.
In recent years, as the three-dimensional viewing apparatus, the increased use of a head mounted display (HMD) has been remarkable. The HMD has left and right virtual image projectors each including a display and an eyepiece so that the image light of the display is directed via the eyepiece to the eye to provide the eye with a virtual image of the display image. Since the images with parallax are presented before the eye, the person wearing the HMD can easily view a stereoscopic image.
In order to view an object stereoscopically with such a stereoscopic system, it is premised that the object is shot by both of the left and right cameras. However, in a three-dimensional camera having its left and right cameras being fixed, since the shooting area common to the left and right cameras is fixed, the shootable area is limited depending on the distance to the object to be shot. When the object to be shot is sufficiently away from the three-dimensional camera, the shooting by both of the left and right cameras is possible. However, the closer the object to be shot is, the smaller the area shootable by both of the left and right cameras is, so that when the object is at a very short distance, it can be shot by one camera but cannot be shot by the other camera.
When the condition is satisfied that the object is shot by both of the left and right cameras, what is next important in the stereoscopic system is how natural the sense of stereoscopy provided by the displayed image is. The sense of stereoscopy of the displayed image depends on the following two factors: the relative directions of the left and right visual axes, i.e. convergence, which directly affect parallax; and the distance from the eye to the image, i.e. dioptric power. Therefore, it is necessary to appropriately set the convergence and dioptric power of the three-dimensional viewing apparatus in accordance with the image to be displayed. Since the image displayed in the viewing apparatus is shot by the three-dimensional camera and the parallax is determined at the time of the shooting, it is also necessary to set the convergence of the three-dimensional camera, i.e. the relative directions of optical axes of the left and right cameras in accordance with the distance to the object. Further, in order that parallax in shooting and parallax in viewing coincide with each other, it is preferable that the convergence of the three-dimensional camera and the convergence of the viewing apparatus coincide with each other. Moreover, although it is a matter of course, it is important that the focus position of the three-dimensional camera is varied according to the distance to the object in order to shoot the object clearly.
As a method to increase the stereoscopically viewable distance range, it is known to set the distance between the left and right cameras to be variable. For example, in Japanese Published Patent Application H5-52116, in a three-dimensional camera provided with left and right taking lenses and left and right image sensing devices, the left and right image sensing devices are arranged to be displaceable in the left and right direction. In the three-dimensional camera of this arrangement, when the distance to the object is short, by setting the distance between the image sensing devices to be wide, the light from the object is imaged on the left and right image sensing devices through the left and right taking lenses.
The above prior art discloses an arrangement of a three-dimensional viewing apparatus having left and right video display devices and left and right eyepieces, where the video display devices are displaceable in the left and right direction. When shooting is performed with an increased distance between the image sensing devices, by setting the distance between the left and right video display devices to be short, the convergence of the viewing apparatus can be set in accordance with the convergence of the three-dimensional camera. In the three-dimensional camera and the three-dimensional viewing apparatus of such arrangements, the range of the distance to the object at which stereoscopically viewable left and right images can be shot becomes wider and the convergence in shooting and the convergence in viewing can be set to substantially coincide with each other.
However, Japanese Published Patent Application H5-52116 discloses neither a specific mechanism to set the convergences of the three-dimensional camera and the three-dimensional viewing apparatus nor a specific method to set the convergences in accordance with the distance to the object. Moreover, the prior art makes no reference to methods to detect the difference in convergence between the camera and the viewing apparatus and to set the convergences so as to coincide with each other.
With respect to the setting of convergence and the adjustment of focus of the three-dimensional camera, for example, Japanese Laid-open Patent Application No. S62-122493 discloses to set the convergences of two cameras with respect to an object to be shot and to calculate the focus position of each camera from the set convergence to perform focusing. Japanese Published Patent Application S60-20734 discloses to perform focusing with respect to an object to be shot and to set the convergence in accordance with the set focus position. However, according to the method to calculate the focus position from the convergence, complicated calculation is necessary, and according to the method to set the convergence based on the focus position, an error in focusing is reflected in the convergence setting, so that an error is also caused in the convergence. In any of the above-described prior arts, the convergence setting and focusing are controlled independently of each other and complicated arrangements are necessary therefor.
Various arts have also been proposed with respect to the setting of the convergence and dioptric power of the viewing apparatus. For example, U.S. Pat. No. 2,955,156 discloses to view a television image with the left and right eyes through an HMD whose convergence and dioptric power are adjustable. However, these adjustments are performed not interlocking with the distance of the stereoscopic image but manually by the viewer, and the convergence and dioptric power are maintained in set conditions unless the viewer operates the HMD.
Japanese Laid-open Patent Applications Nos. S62-115989 and H3-289797 and Japanese Published Patent Application H5-78013 disclose HMDs which set the distance from the eye to the virtual image in accordance with the distance of the displayed stereoscopic image.